Experimental and Modeling Studies of Sr2+and Cs+Sorption on Cryogels and Comparison to Commercial Adsorbents

In this work, two cryogels with the key monomers methacrylic acid and 2-acrylamido-2-methyl-1-propansulfonic acid (named AAC and SAC, respectively) with various functional groups were used as adsorbents for the removal of cesium and strontium ions from aqueous solutions. Kinetics, equilibrium, and column studies were carried out including experiments in different water matrices (ultrapure, tap, and river water) and comparison to commercial adsorbents. AAC reached sorption capacity of 362 mg g-1 for Cs+ and 209 mg g-1 for Sr2+, whereas SAC polymer showed maximum removal capacities of 259 and 211 mg g-1 for Cs+ and Sr2+, respectively. The five cycles of adsorption/desorption experiments showed a maximum of 8% loss of effectiveness for both cryogels. Batch kinetics adsorption data were modeled by using a rigorous diffusional model coupled to a novel fractal-like expression for variable surface diffusivity. The model revealed that the surface diffusivity dependence on time is nonmonotonic, with the occurrence of a maximum. Also, both fluid film and intraparticle transport resistances were shown to be important, with the internal one being more influential. The cryogels and two commercial materials (ion-exchange resin and zeolite) were tested for the removal of Cs+ and Sr2+ in ultrapure, tap, and river water; the results showed that the cryogels exhibit competitive effectiveness.